Pneumatically operated diaphragm motor



' INVEN TOR. fianaiddiaffrzqg jig as.

3 Sheets-Sheet l D. J. GAFFNEY PNEUMATICALLY OPERATED DIAPHRAGM MOTORJune 24, 1952 Flled Aug 17, 1948 June 24, 1952 D. J. GAFFNEYPNEUMATICALLY OPERATED DIAPHRAGM MOTOR 5 Sheets-Sheet 2 Filed Aug. 17,1948 1 INVENTOR.

fiarzaidz/T zzffrz g,

fizz 11%.

June 24, 1952 J GAFFNEY 2,601,511

PNEUMATICALLY OPERATED DIAPHRAGM MOTOR Filed Aug. 17, 1948 3Sheets-Sheet 3 18 ii 97 g 85 105 f0 14; 5

M i I z00 i6); J 5 r 2% III I Y 7 I 2? 7 l 4 54 I l I 17296712 07."flwza-Zd c/faff/a g yw s zm w Patented June 24, 1952 PNEUMATICALLYOPERATED DIAPHRAGM TOR Donald J. Gaifney, Marshalltown, Iowa,

to Fisher Governor Company,

assignor Marshalltown,

Iowa, a corporation of Iowa Application August 17, 1948, Serial No.44,780

This invention relates to a diaphragm operated motor and particularly tosuch a motor for transmitting straight line motion to open and close avalve, governor, or the like.

In the conventional spring loaded diaphragm motor, equipped with a valvedevice sometimes referred to in this art as a positioner, the forceavailable for downward thrust on the valve or governor stem is thepounds per square inch (hereinafter referred to as p. s. i.) output fromthe positioner, which is normally 20 p. s. i., times the area of thediaphragm, minus the compression rate of the spring times the number ofinches it is compressed. In commercial practice, about 75% of thepressure from the positioner is absorbed by the spring at the end of thestroke, and only 25% is available for stem thrust. The only forceavailable for upward thrust at the beginning of the downward stroke isthe initial compression of the spring, which never amounts to more than5 p. s. i. equivalent diaphragm pressure in commercial practice.

The available power in spring loaded diaphragm motors has proveninadequate to handle large single seated controllers, butterfly valvesand even large semi-balanced control valves with extensive pressuredrops. Consequently, there is a definite need for a diaphragm motor withmore power.

One attempted solution to the problem has been a single diaphragm motorwhich is air loaded on top of the diaphragm by a valve device, andloaded on the bottom with a constant air supply set by a smallregulator. The regulator is set at a pressure equal to one-half themaximum output of the valve device and thus has a differential pressureavailable which is equal to one-half the supply pressure to the valvedevice. If the valve device supply pressure is 20 p. s. i., theregulated pressure on the bottom of the diaphragm is set at p. s. i. Ifthe valve device pressure goes to zero, 10 p. s. i. is available forupward force, and if 'the valve device output goes to 20 p. s. i., thereis 10 p. s. 1. available for downward force.

It has been found, however, that such a motor is not suflicientlypowerful for all purposes. Furthermore, a single diaphragm has a certainamount of slack flopping back and forth with equal pressures on both ofits sides. This allows diaphragm head movement resulting in displacementequivalent to the volume in the diaphragm slack without compressing theair in one side of the casing. It is desirable, however, to have thediaphragm movement resisted at all times by the compressibility of theair.

It is an object of the invention to provide a 7 Claims. (Cl. 121-48) 2powerful pneumatically operated diaphragm motor.

It is also an object of the invention to provide such a diaphragm motorin which diaphragm movement is resisted at all times and in which thereis no slack.

It is a further object of the invention to provide a powerful pneumaticdouble diphragm motor.

It is another object of the invention to provide a double diaphragmmotor in combination with a pneumatic reversing valve means or relay;also to provide such a combination for use with a valve device whichadmits or exhausts pressure fluid from one side of the motor and alsooperates the reversing valve.

Another object of the invention is to provide a system wherein thedirection of motion of the pneumatic motor may be reversed by a simplechange in piping connections.

With these and other objects in view, the invention consists in theconstruction, arrange ment and combination of the various parts of mydevice whereby the objects contemplated are attained, as hereinaftermore fully set forth, pointed out in the claims and illustrated in theaccompanying drawings, wherein:

Figure 1 is an elevational view with parts thereof in section, of oneembodiment of the invention;

Figure 2 is a section view of a portion of the valve device shown inFigure 1;

Figure 3 is an elevational View, partially in section, of a secondembodiment of the invention wtih the pneumatic valve means and valvedevice shown in an inverted position from that shown in Figure l; and

Figure 4 is an enlarged sectional view of the reversing relay.

Referring specifically to the drawings, particularly Figures 1 and 2,for a detailed description of the first embodiment of the invention, avalve body is indicated generally at 2| and may be any conventionalcontrol valve, butterfly valve, turbine governor control, or the like,well known in the art. A mechanism for operating the valve or governorincludes a double diaphragm assembly generally indicated at 22,operatinga reciprocating stem 23, a conventional valve device 24 and a reversingvalve means 26 being connected to each other and to the double diaphragmassembly by suitable piping to be described. The reversing valve meansper se is disclosed. and claimed in the copending application of CecilM. Johnson, Serial No. 44,662, filed August 27, 1948, for PneumaticReversing Relays.

The double diaphragm assembly 22 comprises an upper cup-shaped casingmember 21, a lower cupshaped casing member 28 and an intermediateannular or ring shaped member 29. An upper diaphragm 3|, formed ofrubber or synthetic rubber-like material, is clamped between the casingmembers 21 and 29, and a lower rubber or synthetic rubber diaphragm 32is clamped between the casing members 28 and 29. Bolts (not shown) areprovided for retaining the casing members together.

The valve stem 23 is provided with an enlarged portion 33, which isdisposed within the double. diaphragm member 22. The.enlarged-portion33;

of stem 23 engages with a plate 34 disposed on the underside of thediaphragm 3]. A. plate, 3.5 engages with the upper surface of thediaphragm 3| and is clamped to the plate 34 with thediaphragm 3|therebetweeniby a nut 36.

A plate 31 is disposed beneath the enlarged portion 33 in contact withthe upper surface of. the phragm 3.2- A plate 38. clamps the; diaphragm32 between itselfand theplate 3-1. by means of a nut 39 securedhto. stem23. Movement of either diaphragm is, therefore, trans! mitted to theother withoutslack. Atmospheric pressure is present between. the.diaphragmsy3'l. and 32.

The stem 23 extends through the lower casing member 28 and into thevcasing 2|, a packing gland 48 being provided in the lower casing por--tion 28 for the stem 23.

The diaphragms 3| and 32, divide. the double diaphragm 22 into an upperchamber 4|, a lower chamber 42 and an intermediate chamber 43. A.

conduit or pipe 44 communicateswith the upper chamber 4|, and aconduit-45 communicateswith the lower chamber 42, for apurposehereinafter described.

A valve plate 45 supports. levers 4 48 and 49. The lever 41 is.pivotally connected to valve stem 23 at 58. The levers 41 and 48 areconnected together and are pivotally supported on the plate 49 at 52.The lever 49 is pivotally connected to the plate- 46 at and is providedwith a longitudinal slot 52a. The lever 48 isalso'pivotally connected toa block 53- which slides in slot 52a, so that vertical movement of thestem 23 rotates lever 49 about its pivot 5|. A threaded member 55 ispivotally connected to the lever 49 at 54 and has a threaded. abutmentmember 55 thereon which engages with a spring 51, and is adjustable tovary the compressionthereof.

A combination bellows and valve member, generally indicated at 68, isillustrated. in detail in Figure 2 and comprises a main body portion 58having an open ended casing. 59. secured. to one side thereof adjacentspring 51, and a closed; cup-- shaped member 8| secured to theother'side; thereof. A bellows 82 is secured to the side. of the mainbody portion 58 facing the Spring 51, and a.

bellows 63 issecuredto the'other side of the main body portion 58 andis. contained within the easing 6|. 83 in the body portion 58 and engagea plate 66 secured to bellows 63,, and plate: 61 secured to' which inturn has a second valve member 12 on.

its inner extremity. A spring ID engages the inner valve member 12 andthe plate 61 tends tov maintain the valve member 12 seated on its seatl3 formed in body member 58. Apair. of pass g s 14 Rods 84' and 65extend through openings and 15 are also provided in body member 58 incommunication with a conduit 16. The valve member 12 operates to openand close passages 14 and 15, which communicate with conduit 16, in amanner hereinafter described. A conduit H, which communicates with astandard instrument or controller (not shown), also communicates with apassage 18 in body 58, which passage 18 opens into a chamber 19 formedbetween casing member 6| and bellows 83. Chamber 19 is, obviously,hermetically sealed.

Another conduit 8|, which communicates with conduit: '45 and. lowerchamber 42 of the double diaphragm member 22, also communicates with w apassage 82 in body 58, which in turn communicates with passages 83 inbody 58 through which. rods 64 and 65 extend. Conduit 8| is, therefore,in communication with the interior of thezbellows .82. and. 53..

The reversing valve. means 25 comprises a central; body portion84,towhich is secured an up.- per body portion and a lower body Portion.86. A chamber. 81 is formedin the, central body portion of reversing.valve means 25,. and a con.- duit. 88.- communicates with the chamber.8. through. abore 89. at one end thereof and with conduits..-45 and 8|at, the other end thereof.

A diaphragm 9| formedofrubber or synthetic rubber is clamped between theupper portion 85 and the central portion 84 of the reversing valvemeans, and the diaphragm 9.2 is clamped between the-lower portion 85 andthe central portion 840i the-reversing valve means. Bolts may beutilized for retaining the parts together. The effective area ofv thelowerdiaphragm 92 is approximately twice that of the; upper diaphragm 9A stem 93 is secured to the upper and lower diaphragms 9| and 92, in anysuitable manner, the stem 93 being provided with a central passage 94extending therethrough. A valve assembly 98has an upper valve member 95and a lower valve member 95. The lower valve'member 95 normally closesthe upper end of passagg94. The upper body portion 85 of relay 26isprovided with a boss 97, which is internally screw threaded to receivea plug 98. A spring 99' engageswith the plug 98- and with the uppervalve member 95 to normally bias the-valve member 95 into engagementwith its seat |8| surrounding; a passage I in body portion 85, as bestshowninFigure 4. The spring 99 also biases thevalve-member .96 intoengagement with its seat M2 on top of stem 9.3,,as shown in Figure 4.

A passage I83 is provided in the upper body portion 85 of reversingvalve means 26 and communicates at one; end withpipe 44, which in turnis in communication with upper chamber 4| of the double diaphragm member22. The other, end of passage |9.3 communicates with a chamber I94,which is formed above diaphragm 9|. A second passage I is provided inthe upper portion 85 of reversing valve means 26, which communicates atone end with a conduit I95, and at its other end with a chamber H0 abovevalve member 95. The conduit |98 also communicates with conduit l5 andwith a conduit I81, which latter conduit connects with a regulated a rpp y- The lower body portion 85 is provided with an internally threadedboss |09, into which is screwed a hollow plug having a vent H2 in theside thereof. A spring 3 engages. the Closed end of the plug H andengages with a plate 4, which is secured to diaphragm 92, thus tendingto bias stem 93 upwardly into engagement with valve member 95.

Operation of Figures 1 and 2 Referring first to the reversing valvemeans 26, assuming a 20 p. s. i. air supply through conduit I 06, thenwith no pressure at conduit 8|, adjusting screw or plug III is screweddown to adjust the spring II3 until the diaphragm or delivery pressurein conduit 44 is 20 p. s. i. The effective area of diaphragm 92 i twicethat of diaphragm 9|, as stated hereinbefore. If the area of diaphragm9| is equal to y, the area of diaphragm 92 is equal to 2y. If theinstrument or control pressure at 8| is increased 1 p. s. i., there willbe an increase in force on diaphragm 92 equal to 2y and an increase inforce on diaphragm 9| equal to y. This leaves a net unbalanced downwardforce on the diaphragm assembly equal to y and, consequently, theassembly will move, opening the bleed valve 96. This will allow air toescape from the chamber I94 until the pressure on the top of diaphragm9| is reduced 1 p. s. i. The diaphragm assembly will again be in staticbalance, and the bleed valve- 96 closed. Thus, it becomes apparent thatwith every pound increase at 8|, one pound decrease will result at 44.

If there is a l p. s. i. decrease at 8|, this will result in a 1 p. s.i. increase at 44, because the diaphragm assembly of the reversing valvemeans 26 will move upwardly, opening inlet valve 95 and permittingincrease in pressure in chamber I04 and in conduit 44 until thepressures are again balanced, whereupon the inlet valve 95 is closed.

Referring now to the complete air circuit, starting with the air fromthe instrument or controller which enters through conduit 11, increasingair pressure will cause the bellows assembly 62, 63 to be moved to theleft as viewed in Figure 2, which opens the air supply valve "I2allowing air supply pressure entering through conduits I01 and I6 toflow into the chamber formed by the two bellows 62, 63 and throughconduit BI into lower diaphragm chamber 42 of the motor 22. The sameincrease in pressure is also registered in chamber 81 of reversing valvemeans 26 which, as explained above, causes an unbalance in the relaydiaphragm assembly and causes it to move downwardly allowing air toescape from chamber I04 through passage 94 and bleed outlet II2. Thislowers the pressure in the chamber 4| of the motor 22 an amountequivalent to the rise in pres sure in the chamber 42 of motor 22. Thereis now an unbalanced force on the main diaphragm assembly 3|, 32 whichcauses the valve stem 23 to move upwardly. This supplies compression tothe spring 51 through the levers 41, 48 and 49, which balances theincrease in pressure on be1- lows assembly 62, 63, causing supply valveI2 to again close. This places the system again in balance. If, due tohysteresis in the diaphragm assembly 3|, 32, sticking in the stuilingbox 40 or unbalanced pressure forces on the valve or governor beingoperated, the valve stem 23 does not move immediately, air Will continueto bleed through the inlet valve I2, consequently increasing airpressure in the chamber 42 and decreasing pressure in the chamber 4|until the valve stem 23 moves or until the pressure in chamber 42 hasincreased to the equivalent of the air supply, that is, 20 p. s. i., andthe air pressur in chamber 4| has reached zero. This makes available formoving the valve stem 23 a force equivalent to the product of thediaphragm area 32, times the supply pressure. For example, if thediaphragm area is 100 square inches and the air supply is 20 p. s. i.,

there is a 2000 pound force available to move the valve stem 23.

Upon a decrease of pressure from the instrument or controller throughconduit 11, the bellows assembly 62, 63 will move to the right as viewedin Figure 2. Since the inner valve I2 is seated at I3, it cannot movefurther to the right. Consequently, the left hand bellows head 61 breaksaway from bleed valve 69, opening the bleed port 68 and allowing air tobleed from the chamber formed by the bellows 62, 63. This decreases thepressure in chamber 81 of reversing valve means 26 and in chamber 42 ofthe motor 22. The decrease in pressure in chamber 81 causes an increasein pressure in chamber 4| of motor 22, as explained above. The unbalanceon the diaphragm assembly 3|, 32 will now cause the valve stem 23 tomove downwardly, which, through levers 41, 48 and 49, will decrease theloading on spring 51 until the spring load again balances the pressureload from the instrument or controller in the chamber formed by bellows63 and cup member BI, thus closing bleed valve 69 and placing the systemagain in balance.

Description of Figure 3 Referring now to Figure 3 for a description ofthe second embodiment of the invention, it is first noted that the valvedevice 24 and the reversing valve means 26 are identical with thatdescribed with respect to Figures 1 and 2, except that they areinverted. Furthermore, the bellows assembly shown in Figure 2 isidentical in Figure 3 as is the valve or governor to be operated. Wherethe parts are the same, the same numbers have been given in Figure 3 asin Figures 1 and 2. *One of the advantages of the invention is that bymerely inverting the valve device 24 and reversing valve means 26 andmaking the proper piping connections, the direction of operation ofvalve stem 23, upon increase and decrease in instrument or controlpressure, may be reversed. In the em bodiment shown in Figure 3, theprinciple of operation of the motor, which is given number I22, is thesame as discussed with respect to Figures 1 and 2.

The motor I22 comprises an upper cupshaped casing member I2'I, a lowercup-shaped casing member I28 and an intermediate annular casing memberI29, having a wall I45 extending across the annular member I29 with anopening I30 centrally thereof. A diaphragm I 3| of rubber or the like isclamped between the casing members I21, I 29, and a similar diaphragmI32 is clamped between the casing members I28 and I29.

A reciprocating sleeve I33 surrounds a stem I23 within the casing I22,and is adapted to slide in opening I39 in the partition I45. The sleeveis secured at its upper end to a plate I34, which, with a plate I35 andnut I36, clamps the diaphragm I3| to the stem I23 and sleeve I 33. Thesleeve I33 is secured at its lower end to a plate I37, which, with aplate I38 and nut I39, secures the sleeve I33 and stems 23 and I23 tothe lower diaphragm I32. A stufiing box I49 is provided in the lowercasing member I28 for the valve stem 23.

There is thus formed in the motor I22 an upper air chamber I4! and alower air chamber I 42. A conduit I44 opens into the chamber I 4| andcommunicates with conduit 45 and 8|. Also formed within the casing I22is a chamber I46 between diaphragm |3| and partition I45, and a chamberI41 between diaphragm I32 and partition I45.

' A suitable plug I48 is provided in the top casing member I21, and aneedle valve I49 is provided in casing member I29, which is alsoprovided with passages II and I52 communicating with chambers I45 andI41, respectively, when valve I49 is open. The two chambers I46 and I41are filled with a liquid having a relatively low freezing point, and theneedle valve I49 restricts the passage between the chambers I46 and I41.The diaphragm spacer or sleeve I33 is a closely machined fit in thepartition I45. In order for the diaphragm assembly I3I, I32 to move,liquid must be displaced between chambers I46 and I through thepassagesI5I and I52. This gives the diaphragm assembly a high degree ofstability, which may be controlled by the needle valve I49.

Operation of Figure 3 The operation of the device is exactly the same asthat described with respect to Figures 1 and 2, except that upon anincrease in instrument or control pressure in conduit 11, the valve stem23 moves downwardly, while a decrease in instru-- ment or controlpressure causes the valve stem 23 to move upwardly.

From the foregoing, it will be apparent that I have provided a doublediaphragm motor valve which is extremely powerful, and that the motorvalve, in combination with a pneumatic reversing valve means, providesimproved operation and aiiords, .a reversal of movement in a very simplemanner.

Some changes may be made in the construction and arrangement of theparts of my device without departing from the real spirit and purpose ofmy invention, and it is my intention to cover by my claims any modifiedforms of structure or use of mechanical equivalents which may bereasonably included within their scope without sacrificing any of theadvantages thereof.

I claim as my invention:

1. In a pneumatic system, the combination of a pneumatic motor forimparting reciprocating movement to a member, a valve device adapted toeffect admission of fluid pressure to said motor and exhaust fluidpressure therefrom, a

reversing valve means for said motor controlled by said valve device,said motor including a casing, two spaced diaphragms scanning the casingto form therewith a first chamber, a second chamber and an intermediatespace between the diaphragms, means for securing said diaphragmstogether and to the member to be reciprocated, a supply of fluid underconstant pressure, fluid connections between said constant pressuresupply and said valve device and reversing valve means, a supply offluid under variable pressure connected to said valve device, fluidconnections to said first and second chambers, one of said lastconnections communicating with the reversing valve means and the otherwith said valve device, and movable valve members and passages in saidreversing valve means and said. valve device so arranged that anincrease in said variable pressure fluid supply effects an increase ofpressure in one of said.

chambers and a decrease in pressure in the other of said chambers, andvice versa when said variable pressure fluid supply decreases.

2. A pneumatic motor for imparting reciprocating movement to a member,said motor comprising a closed casing, said casing including an 8, uppermember, a lower member and an intermediate member, said intermediatemember providing a partition, a first diaphragm extending across saidcasing above said partition and being clamped at its periphery betweenthe upper and intermediate casing members, a second diaphragm extendingacross said casing below said partition and being clamped at itsperiphery between the lower and intermediate casing members, saiddiaphragms with the partition and casing forming four chambers, namely,an upper chamber above the first diaphragm, a lower chamber below thesecond diaphragm, a chamber between the first diaphragm and thepartition, and a chamber between the second diaphragm and the partition,said chambers between the diaphragms and the partition being filled withliquid, a connecting passage between the chambers filled with liquid,and means for connecting said diaphragms together and to the member tobe reciprocated, said connecting means including a sleeve surroundingsaid member to be reciprocated and extending through an opening disposedcentrally of said partition, said sleeve being in contact with saidmember to be reciprocated adjacent the portion thereof which extendsthrough said partition and also closely fitting the opening in saidpartition whereby any passage of fluid between the two chambers throughsaid opening is substantially prevented.

3. A pneumatic motor for imparting reciprocating movement to a member,said motor comprising a closed casing, said casing including an uppermember, a lower member and an intermediate member, said intermediatemember providing a partition, a first diaphragm extending across saidcasing above said partition and being clamped at its periphery betweenthe upper and intermediate casing members, a second diaphragm extendingacross said casing below said partition and being clamped at itsperiphery between the lower and intermediate casing members, saiddiaphragms with the partition and casing forming four chambers, namely,an upper chamber above the first diaphragm, a lower chamber below thesecond diaphragm, a chamber between the first diaphragm and thepartition, and a chamber between the second diaphragm and the partition,said chambers between the diaphrag-ms and the partition being filledwith liquid, and means for connecting said diaphragms together and tothe member to be reciprocated, a connecting passage between said thirdand fourth chambers extending through said partition and a restrictingvalve for controlling the fiow of fluid between said chambers throughsaid passage.

4. A pneumatic motor for imparting reciprocating movement to a member,said motor comprising a closed casing, said casing including an uppermember, a lower member and an intermediate member, said intermediatemember providing a partition, a first diaphragm extending across saidcasing above said partition and being clamped at its periphery betweenthe upper and intermediate casing members, a second diaphragm extendingacross said casing below said partition and being clamped at itsperiphery betweenthe lowerand intermediate casing members, saiddiaphragms with the partition and casing formingv four chambers, namely,an upper chamber above the first diaphragm, a lower chamber below thesecond diaphragm, a chamber between the first diaphragm and thepatition, and a chamber between the second diaphragm and the partition,said chambers between the diaphragms and the partition being filled withliquid, means for connecting said diaphragms together and to the memberto be reciprocated, said connecting means including a sleeve surroundingsaid mem ber to be reciprocated and extending through an openingdisposed centrally of said partition, said sleeve being in contact withsaid member to be reciprocated adjacent the portion thereof whichextends through said partition and also closely fitting the opening insaid partition whereby any passage of fluid between the two chambersthrough said opening is substantially prevented, a connecting passagebetween said third and fourth chambers extending through said partition,and a restricting valve for controlling the flow of fluid between saidchambers through said passage.

5. In a pneumatic system, the combination of a pneumatic motor forimparting reciprocating movement to a member, a valve device adapted toefiect admission of fluid pressure to said motor and exhaust fluidpressure therefrom, a reversing valve means for said motor controlled bysaid valve device, said motor including a casing, two spaced diaphragmsspanning the casing to form therewith a first chamber, a second chamberand an intermediate space between the diaphragms, means for securingsaid diaphragms together and to the member to be reciprocated, a supplyof fluid under constant pressure, fluid connections between saidconstant pressure supply and said valve device and reversing valvemeans, a supply of fluid under variable pressure connected to said valvedevice, fluid connections to said first and second chambers, one of saidlast connections communicating with the reversing valve means and theother with said valve device, and movable valve members and passages insaid reversing valve means and said valve device so arranged that anincrease in said variable pressure fluid supply effects an increase ofpressure in one of said chambers and a decrease in pressure in the otherof said chambers, and vice versa when said variable pressure fluidsupply decreases, said diaphragms having substantially equal effectiveareas.

6. In a pneumatic system, the combination of a pneumatic motor forimparting reciprocating movement to a member, a valve device adapted toeiTect admission of fluid pressure to said motor and exhaust fluidpressure therefrom, a reversing valve means for said motor controlled bysaid valve device, said motor including a casing, two spaced diaphragmsspanning the casing to form therewith a first chamber, a second chamberand an intermediate space between the diaphragms, a partition extendingacross the casing in the space between the diaphragms, means forcontrollably connecting the spaces formed between the diaphragms and thepartition, means for securing said diaphragms together and to the memberto be reciprocated, a supply of fluid under constant pressure, fluidconnections between said constant pressure supply and said valve deviceand reversing valve means, a supply of fluid under variable pressureconnected to said device, fluid connections to said first and secondchambers, one of said last connections communicating with the reversingvalve means and the other with said valve device, and movable valvemembers and passages in said reversing valve means and said valve deviceso arranged that an increase in said variable pressure fluid supplyeffects an increase of pressure in one of said chambers and a decreasein pressure in the other ofsaid chambers, and vice versa when saidvariable pressure fluid supply decreases.

7. In a pneumatic system, the combination of a pneumatic motor forimparting reciprocated movement to a member, a valve device adapted toefiect admission of fluid pressure to said motor and exhaust of fluidpressure therefrom, and a reversing valve means controlled by said valvedevice, for said motor, said motor including a casing, two spaceddiaphragms spanning the easing to form therewith first and secondchambers, a partition extending across the casing between saiddiaphragms, means extending through the partition for securing saiddiaphragms together and for imparting movement thereof to the member tobe reciprocated, a supply of fluid under constant pressure, saidconstant pressure supply being connected to said valve device and tosaid reversing valve means, a supply of fluid under variable pressureconnected to said valve device, fluid connections to said first andsecond chambers, one of said last connections communicating with thereversing valve means and the other with said valve device, saidreversing valve means being effective to increase the pressure in one ofsaid chambers when the pressure in the other decreases and to decreasethe pressure in said one chamber when the pressure in the otherincreases, the space between both of said diaphragms and said partitionbeing filled with liquid, a passage between said liquid filled chambersaffording passage of liquid therebetween and a restricting valve in saidpassage to control the flow of liquid therethrough.

DONALD J. GAFFNEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,937,244 Pelton Nov. 28, 19332,092,019 Randel Sept. 7, 1937 2,372,345 Temple Mar. 27, 1945 2,376,671Dodson May 22, 1945 2,382,941 Moore Aug. 14, 1945 2,400,048 Jones May 7,1946 FOREIGN PATENTS Number Country Date 14,235 Germany -1 of 1881 3,058Great Britain of 1884 644,689 Germany June 14, 1937

